VP-4
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ABOUT VP-4
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About VP-4
The VP-4 measures air temperature, relative humidity (RH), vapor
pressure, and barometric pressure. A microprocessor within the VP-
4 calculates vapor pressure from the RH and temperature measure-
ments. The VP-4 uses a sensor chip to measure both air temperature
and RH and a secondary chip to measure barometric pressure. Each
VP-4 has calibrations coefficients stored on board. The calibration
coefficients are applied before data are output. Air temperature, rel-
ative humidity, vapor pressure, and barometric pressure are output
from the sensor using an RS232 (TTL) string and the common SDI-
12 communication protocol.
The VP-4 sensor is packaged in a rugged Delrin housing with the
sensor electronics potted in marine grade polyurethane encapsulant.
The RH/T sensor chip is protected by a hydrophobic porous Teflon
filter that is water and dust proof, but has an extremely high vapor
conductance allowing fast sensor equilibration with the surrounding
atmosphere. An additional stainless steel screen protects the Teflon
filter and RH/T sensor from impact and abrasion. The rugged design
allows the VP-4 to withstand long term exposure to hostile condi-
tions, making it ideal for a wide range of applications including stan-
dard meteorological monitoring, evapotranspiration measurement,
greenhouse monitoring and control, concrete moisture monitoring,
and building humidity monitoring for mold prevention and remedia-
tion.
2.1
Specifications
Relative Humidity
Range: 0 to 100% RH
Resolution: 0.1% RH
Accuracy: Sensor measurement accuracy is variable across a range
of RH. Refer to the chart in Figure 1 to determine the accuracy
specification for the VP-4 sensor:
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